DC-arc furnaces are used as new smelting units for the production of Fe and ferro-alloys. In order to obtain a better understanding of electrophoretic phenomena occurring in the slag phase during the smelting process, the electrophoresis data for the TiO₂ rich slag are examined. The discussion is extended to the determination of metal drop velocity in the slag phase. Results including reduction results obtained in the titanium stags and Cu-secondary stags are presented. The effect of polarity change on the reduction degree of stags in the arc furnace is discussed in theoretical and experimental viewpoints.